The present invention relates generally to a method for writing servo sector patterns on a data disk storage device, and more particularly, to self-servo writing of servo sector patterns on a data disk storage device using a reference pattern on a surface of a data disk.
In many processing and computing systems, magnetic data storage devices, such as disk drives are utilized for storing data. A typical disk drive includes a spindle motor having a rotor for rotating one or more data disks having data storage surfaces, and an actuator for moving a head carrier arm that supports transducer (read/write) heads, radially across the data disks to write data to or read data from concentric data tracks on the data disks.
In general, a magnetic transducer head is positioned very close to each data storage surface by a slider suspended upon an air bearing. Typical clearance between a smooth disk surface and the slider is about one microinch, or less. The close proximity of the head to the disk surface allows recording of very high resolution data and servo patterns on the disk surface. Servo patterns are typically written with uniform angular spacing of servo sectors and interleaved data sectors or blocks. An example servo pattern includes circumferentially sequential, radially staggered single frequency bursts. Servo patterns provide the disk drive with head position information to enable the actuator, such as a rotary voice coil positioner, to move the head from starting tracks to destination tracks during random access track seeking operations. Further, the servo patterns provide the disk drive with head position information to enable the actuator to position and maintain the head in proper alignment with a track centerline during track following operations when user data is written to or read from the available data block storage areas in concentric data tracks on the disk surface.
Data transducer heads currently in use employ dual elements. An inductive write element having a relatively wide recording gap is used to write information into the data tracks, and a read element such as a xe2x80x9cgiant-magneto-resistive sensorxe2x80x9d having a relatively narrow playback gap is used to read information from the data tracks. With this arrangement, data track densities equaling and exceeding e.g. 30,000 tracks per inch are possible.
In a standard manufacturing process the head disk assembly (HDA) of the disk drives are assembled in a clean room environment, then transported to a specialized servowriter station where the drive is mounted to a stabilized metrological measurement system. A customized drive electronic assembly then writes a servo reference track, from which the embedded servo format is created. The drive modules are then assembled to the HDA and are moved to a self scan station where the drives are tested for reliable servo operation. Block errors, drive defects, drive specific control tracks and other information is written to the media at this station. If the drive fails the self-scan tests it is either reworked or scrapped at this late manufacturing stage.
Conventionally, servo patterns are written into the servo sectors of each disk using a servowriter at a point in the drive assembly process before the hard disk unit is sealed against particulate contamination from the ambient. A servo writer is a complex and expensive manufacturing unit, typically stabilized on a large granite base to minimize unwanted vibration and employing e.g. laser interferometry for precise position measurements. The servo writer typically requires direct mechanical access to the head arm, and includes a fixed head for writing a clock track onto a disk surface.
Because of the need for direct access to the interior of the hard disk assembly of each disk drive unit, the servo writer is typically located within a xe2x80x9cclean roomxe2x80x9d where air is purged of impurities that might otherwise interfere with operation including the servo writing process or in normal usage after manufacturing. Further, such conventional servo-writing methods are very time consuming. In one example, a disk drive having two disks with four data storage surfaces can require three servo-writer-controlled passes of the transducer head over a single track during servo writing, consuming a total servo writing time as long as 13.2 minutes. Thus, servo writing using servo writers in clean rooms requires both considerable capital investment in the manufacturing process and severe time penalties in the manufacturing process attributable to servo writer bottlenecks. Further, as track densities increase with evolving hard disk designs, servo writers become obsolete, and have to be replaced, or upgraded, at considerable capital expense.
An attempt to alleviate the above shortcomings is directed to servo writing a master pattern at full resolution on one surface of a master disk during a pre-assembly operation. Then, a master disk with the master pattern is assembled with other blank disks into a disk drive unit. After the disk drive unit is sealed against the ambient, the master servo pattern of the master disk is used as a reference by the disk unit in self-writing embedded sector servo patterns on each data surface within the enclosed unit. Finally, the master pattern is erased, leaving the disk drive unit with properly located embedded servo sector patterns on every surface, including the surface which originally included the master pattern. An example of this servo writing method is described in U.S. Pat. No. 5,012,363 to Mine et al, entitled: xe2x80x9cServo Pattern Writing Method for a Disk Storage Devicexe2x80x9d. However, a disadvantage of such a method is that certain repeatable run out information must be removed during the self-servo write operation. Another disadvantage of such a method is that a number of expensive servo writers are still required to write the master patterns on the master disks.
A self-servo writing method which eliminates the need for such servo-writers is described in commonly assigned U.S. Pat. No. 5,668,679 to Swearingen et al., entitled: xe2x80x9cSystem for Self-Servo writing a Disk Drivexe2x80x9d, the disclosure thereof being incorporated herein by reference. That method essentially comprises the steps of writing a clock track at an outside diameter (OD) recording region of a first disk surface of a disk drive having multiple storage surfaces, tuning an open-loop seek from the OD to an inside diameter (ID) recording region to develop a repeatable seek profile, and recording a plurality of high frequency spiral tracks from the OD to the ID, each spiral track including embedded (e.g. missing bit) timing information. Then, spiral track provided peak data, and missing bit data, are read back. A voltage controlled oscillator is locked to the timing information to track disk angular position. As the head is then moved radially from OD to ID the detected spiral peaks shift in time relative to a starting (index) mark, although the timing information does not shift. Embedded servo sectors can then be precisely written across the data storage surface by multiplexing between reading spirals and writing servo sectors (wedges). After the integrity of the wedges has been verified, the spirals are erased (overwritten with user data). While this method is satisfactory, challenges remain in generating and recording an accurate clock pattern on the first disk surface. Further, the time period required to produce the master position pattern on the first disk surface can be lengthy.
There is, therefore, a need for an improved self-servo writing method in disk drives which reduces self-servo writing times, is simpler to implement and does not require servo-writers.
The present invention satisfies these needs. In one embodiment, the present invention provides a method and system for self-servo writing a disk drive by transferring a servo reference pattern by magnetic printing onto at least one storage surface of a reference disk, wherein a resulting printed reference pattern includes embedded servo information providing servo timing and transducer head position information; assembling the disk drive including the steps of installing at least said disk into the disk drive and enclosing said disk and the data transducers within a housing sealed against particulate contamination from an eternal ambient environment; reading the printed reference pattern from said disk via at least one transducer head to generate a readback signal; sampling the readback signal at a sampling rate to generate a sampled signal; processing the sampled signal waveform specturm to generate a recovered signal including the embedded servo information and a fundamental frequency of the sampled signal; using the servo information from the recovered signal to precisely position and maintain the data transducers at concentric track locations of disk storage surfaces; and self-writing disk drive servo patterns onto the storage surfaces at the concentric track locations with the data transducers in accordance with disk drive servo pattern features.
The present invention allows the disk drive to be fully assembled and tested in one location at one time. In addition it eliminates the requirement for the servowriter stations which occupy a large portion of the clean room factory floor. In one embodiment, the present invention utilizes an architecture for the read and write sections of a disk drive read/write channel and controller which allows the extraction of embedded servo reference timing from a printed reference pattern and a technique to replicate that timing onto the surface of the embedded product servo format.
According to another example method and system according to the present invention, a preformatted magnetic reference pattern is applied to one or more surfaces of disk media and are then assembled, using the standard manufacturing process, into the HDA. A phase extraction process extracts pattern phase information from the reference pattern, and another process eliminates any mechanical runout (i.e., eccentricity) due to standard assembly, using a combination of hardware and software signal processing techniques. The entire system structure is contained within the disk drive channel/controller design and requires no external devices or process steps during the disk drive manufacturing process. This allows the disk drives to be moved from the assembly area to the selfscan area where they are formatted and tested without the need to maintain and support a separate external servowriter process. It also allows the additional capability of detecting and correcting servo defects when the user data area is qualified during self scan.
The present invention helps reduce the manufacuturing costs of a disk drive assembly by eliminating the servowrite manufacturing process. The performance of the disk drive is unaffected in terms of user bit error rate, reliability or overall capacity. The lower disk drive manufacturing costs also increases profit margins.